Centrifugal rotational molding apparatus



Dec. 31, 1963 A. MARLO 3,115,679

CENTRIFUGAL ROTATIONAL MOLDING APPARATUS Original Filed May 26, 1959 I 5Sheets-Sheet 1 IN VENTOR.

ARVID MARLO z zz Mm, haw

ATT'YS Dec. 31 1963 A. MARLO 3,115,679

CENTRIFUGAL ROTATIONAL MOLDING APPARATUS Original Filed May 26, 1959 5Sheets-Sheet 2 INVENTOR: ARVID MARLO I (at ma ATT 'YS Dec. 31, 1963 A.MARLO CENTRIFUGAL ROTATIONAL MOLDING APPARATUS Original Filed May 26,1959 5 Sheets-Sheet 3 ARVID MARLO ATT'YS 5 Sheets-Sheet 4 @GE m OE A.MARLO CENTRIFUGAL ROTATIONAL MOLDING APPARATUS Dec. 31, 1963 OriginalFiled May 26, 1959 mvmqrron: ARVID ARLO ATT'YS Dec, 31, 1963 A. MARLO3,115,679

CENTRIFUGAL ROTATIONAL MOLDING APPARATUS Original Filed May 26, 1959 5Sheets-Sheet 5 UNLOAO INVENTOR.

REFILLING United States Patent 3,115,679 CENTREFUGAL RQTATIGNAL MQLDINGARPARATUS Arvid Marlo, 3102 N. heilield, Chicago 13, ill. @riginalapplication May 26, 1959, Ser. No. 815,974, now Patent No. 3,648,896,dated Aug. 14, 1962. Divided and this application May 31, 1962, Ser. No.199,129 7 Claims. (Cl. 18-26) This invention relates in general to acentrifugal rotational molding apparatus, and more particularly to anapparatus for producing hollow articles from a thermosetting plastic.

Heretofore, apparatus for molding hollow plastic articles has beencomplex in structure, which increased the maintenance requirements, andwhich necessitated an expensive machine. Further, all molding machinesheretofore of this type have rotated the molds on divergent axes duringcuring of the moldable material. Still further, the machines heretoforehad a limited capacity which resulted in the production of a relativelyexpensive product.

Accordingly, it is an object of this invention to obviate theabove-named difliculties, and provide an improved apparatus for makinghollow articles.

Another object of this invention is in the provision of a simpleapparatus that can be economically manufactured for the production ofhollow plastic articles.

Still another object of this invention resides in the provision of anapparatus for producing hollow plastic articles which is capable ofhandling a plurality of molding units at one time in order to give ahigh production of articles.

Other objects, features and advantages of the invention will he apparentfrom the following detailed disclosure, taken in conjunction with theaccompanying sheets of drawings, wherein like reference numerals referto like parts, in which:

FIG. 1 is a front perspective view of the apparatus for molding articlesaccording to the present invention;

FIG. 2 is a rear perspective view of the apparatus of FIG. 1;

FIG. 3 is a view showing a molding unit according to the presentinvention and how it may be associated with the carriages or racks ofthe molding apparatus of FIGS. 1 and 2;

FIG. 4 is a perspective view of the molding unit of FIG. 3 andillustrating the molding unit and the locking bars in open position;

FIG. 5 is an enlarged transverse sectional view of a mold, takensubstantially along line -55 of FIG. 3;

FIG. 6 is an enlarged transverse sectional view taken through a modifiedmold according to the present invention;

FIGS. 7 to are sectional views taken through molds and illustrating thesteps in performing the method of molding to produce hollow plasticarticles according to the present invention; and

FIG. 16 is a perspective view of a modified apparatus for molding hollowplastic articles wherein the carriages for supporting the molding unitsare carried on an endless conveyor.

Referring now to FIGS. 1 and 2, particularly, the centrifugal rotationalmolding apparatus of the present invention includes an oven 17 havingfront and back 3,ll5,679 Patented Dec. 31, 1963 Walls 18 and 19',respectively, side or end walls 20, 2t), and a top wall 2'1. A bottommay or may not be provided for the oven, inasmuch as the floor uponwhich the oven would set would define a bottom. The oven is heated by aplurality of longitudinally spaced fuel burners 22 arranged along thelower portion :of the oven and interiorly thereof, as seen in FIG. 2.These fuel burners are attached to a common fuel line 23 which connectsto a line 24:- extending from the oven and leading to a source of fuelsupply. It may be appreciated that other types of heating elements maybe provided without varying the scope of the present invention.

Adjacent the upper end of the oven, and mounted in the back wall 19 area plurality of longitudinally spaced bearing members 25, each of whichrotatably supports a shaft having one end 26 extending into the interiorof the oven and the other end 27 extending externally of the oven. Allof the shafts are arranged along a single horizontal plane.

A rack or carriage, generally designated by the numeral '28, iscantileverly supported by the shaft end 26 within the oven. The racksare adapted to removably receive a molding unit 29, FIGS. 1 and 3. Eachrack includes a solid back wall 36 having extending from the fourcorners thereof angle irons 31 which are rectangularly spaced andarranged to define an open framework for slidably receiving a moldingunit 2-9. The angle irons 31 extend parallel to each other andsubstantially perpendicular to the back wall Call. The length of theangle irons 31 is determined by the distance between the front and backWalls l8 and 19, respectively, of the oven. The longitudinal axes of theracks 28 extends subst-antially perpendicular to the longitudinal axisof the oven 17. Flanges 32 project substantially perpendicularly fromthe back Wall 36 of each rack 23- and are arranged between the angleirons 31 in order to enhance the strength of the racks. Thus, a moldingunit 29 may be easily slidably inserted into the open end of a rack 28,and removed therefrom.

Opposite the open end of each rack 28 is an opening 33 in the front wallill to provide access to insertion and withdrawal of the molding units29 from the oven and racks. Each opening is normally covered by a door34 hingedly secured to the front wall at its upper end and at the upperend of the opening at 35. Thus, the doors 3d swing outwardly andupwardly to uncover the openings 33. Any suitable means may be providedfor holding the doors 34 in the open position while manipulating amolding unit 29 through the opening.

The shaft ends 27 which extend externally of the oven have securedthereon adjacent their very ends pinion gears 36. All of the piniongears are in engagement with an elongated rack gear 37 slidablysupported along an elongated guide channel 3%. The guide channel 38 issupported by a plurality of upstanding standards 3-9 which support theguide channel on the floor. One end of the rack gear 37 is secured to apiston rod of a double-acting pneumatic cylinder ill that is supportedabove the floor by a stand 41. Thus, operation of the pneumatic cylinderill reciprocates the rack gear 37 to rotate the pinion gears 36 and theracks 28. The length of movement of the piston rod in the pneumaticcylinder 40' is such as to rotate the racks 28 through 186 revolutions.A timer 42 of any suitable type is mounted on the cylinder stand 3, 41for controlling operation of the pneumatic cylinder 49 and therebydetermines the interval of time between reciprocation thereof.

A cooling table, generally designated by the numeral 4-3, projects fromthe front wall 13 just below the opening 33 and is supported from thefloor by a plurality of legs 44. In alignment with each opening 33, arecessed opening 45 is provided in the table 43 and sized to re ceive amolding unit 29 as s iown in FIG. 1. A blower 46 is provided for eachrecessed opening 45 and spaced below the table to generate cooling airand drive it upwardly through the funnel-shaped ducts 47 and the opening for cooling the molding units when they are removed from the oven.

Accordingly, a plurality of molding units may be placed in the oven 17for molding and curing of hollow plastic articles at one time, andlikewise the molding units may be arranged on the cooling table 43 atone time for cooling thereof prior to opening of the molds and removalof the hollow plastic articles. While only nine stations are illustratedin the apparatus as shown in FIG. 1, it can be appreciated that agreater or lesser number may be provided to accommodate the desires ofthe user.

Referring now particularly to FIGS. 3, 4 and 5, each molding unit 29includes upper and lower mold supporting plates 48 and 49, generallyrectangular in shape, which may support therebetween any number of moldsdesired. A plurality of molds d are carried by the mold suppo'rt ingplates 43 and 4%. The molds 59 are sectional and formed from halveswhich include an upper section Sit and a lower section 52 havinginternal surfaces shaped to define a substantially ovalshaped hollowarticle. The mating edges of the sections 51 and 52 are complimentallygrooved, as indicated at 53, FIG. 5, to guide the mating elationtherebetween and provide a smooth inner wall surface for producingseamless hollow plastic articles.

The lower mold section 5?; is supported on the lower plate 49 by a stem54, which has a reduced portion 55 at its very end thereby defining anannular shoulder 56. The reduced portion 55 is received in a blind bore57 provided in the lower plate 49, and the shoulder 56 bottoms againstthe upper surface of the plate 49 encircling the bore 57. A stud bolt 5%fixedly secures the stem 54 to the plate 49, whereby the lower moldsection 52 is then fixedly mounted to the lower plate 49.

The upper mold section 51 is resiliently mounted on the upper moldsupporting plate 48 by means of a stem 59 projecting from the upper endof the mold section and slidably received in a bore 6% extending throughthe upper plate. A coil spring 61; encircles the stem 59', and bottomsat one end on the top of the mold section 51 and at the other end on theunder surface of the upper plate 48 to resiliently bias the mold section51 downwardly and towards the lower mold section 52. A lock ring 62 isprovided to be secured to the upper end of the stem 59 and on the upperside of the plate 48 in a recessed portion 63 to limit the downwardmovement of the stem 59 from the plate 48.

Runners 64 are provided along the opposite edges of the upper plate 43on the upper side thereof, and runners as are provided along theopposite edges and on the lower side of the lower plate 49 in order toproperly size the molding unit for fit into the rack 28. If larger moldsare used than the molds 5%, the size of the runners may be decreased inorder to still properly fit within the racks 28. On the other hand, ifthe mold size is decreased from that shown, the runner size can beincreased in order to fit in the racks 28. Thus, it may be appreciatedthat any size mold within certain limits may be utilized, and Will bereceived within the racks 28 of the molding apparatus 7.

In order to lock the upper plate 43 with its mold sections 51 to thelower plate 49 with its mold sections 52, longitudinally extendinggrooves 65a are provided in the opposite edges of the upper plate 33,and longitudinally extending grooves as are provided in the oppositeedges of the lower plate to receive flanges 6'7 of locking plates 62* asseen in PEG. 3. The locking plates are substantially channelshaped andhaving the flanges 67 at the opposite edges extending substantiallyperpendicularly to the main portion and for engagement in the grooves ofthe upper and lower mold supporting plates. The distance between theflanges 67 is such that in 0rd?! engage them in the grooves of "he moldsupporting plat s, it is necessary to first press the mold supportingplates together against the biasing of the springs 61, whereby when theyare released, the flanges will frictionally locl; with the grooves, andthereby resiliently hold the mold sections 51 and 52 together in propermating positron, Enlarged holes 6% are provided in the locking plates 68in order to permit circulation of air through the molding unit andaround the molds 5%. When the molding units 29 are set on the coolingtable 43, they are, in effect, set on edge whereby the circulation ofair generated by the blowers as will enter through one of the lockingplates of; and be dispersed about the molds 5t) and exit through theother locking plate and through the opposite ends of the molding unit.When placing the molding unit 29 into the racks 28 of the moldingapparatus 17, they will be placed right side up or with the upper andlower mold supporting plates extending horizontally.

A modified type of molding unit, generally designated by the numeralZhA, is shown in MG. '6, which differs in the type of molds used andsupported between the upper and lower mold supporting plates 43 and 33.-In this embodiment, the molds which may be designated by the numeralStlA are not individually mounted to the supporting plates, but arejoined together by webbing 7% to define an upper sheet 71 of cavities 72and a lower sheet '73 of cavities 74, which mate together to define themolds for each of the hollow articles, as seen in FIG. 6 The lower sheet73 of cavities is fixed to the lower mold supporting plate 49 by aplurality of stems 7 5 extending down wardly from some of the cavities,and stud bolts 76, in a manner similar to that of the embodiment inFIGS. 3 to 5. Similarly, stems 77 extend upwardly from some of thecavities 72 of the upper sheet 71 and are slidably received in bores 7 8provided in the upper plate 48. Coil springs 79 are arranged between theupper plate and the mold cavities and locking rings 30 are provided toprevent the stems 77 from leaving the plate 48. Accordingly, the uppersheet 71 is resiliently mounted to the upper mold supporting plate 48.Therefore, the cavities '72 in the upper sheet 71 will mate with thecavities 74 in the lower sheet 73 when the upper and lower supportingplates 48 and 49 are placed together and the cavities will be biasedtoward each other in the same manner as in the embodiment of FIGS. 3 to5.

The molding apparatus of the present invention is illustrated in FIGS. 1and 2, wherein the racks 28 are supported on stationary bearings, andwhere there may be need for still increased production, the racks 28 m ybe mounted on an endless conveyor 81 as seen in 16 which carries theracks through an oven 82 and a cool chamber 83. The endless conveyor 81includes a chain mounted around spaced sprockets M and 85. The sprocket85 constitutes the drive sprocket and is mounted on a drive shaft 86having a sprocket 87 thereon in meshing engagement with an endless drivechain 55 A sprocket 89 is also in meshing engagement with the chain 8-8and is mounted on an output shaft of a combination motor reduction gearassembly 90'. Thus, the endless conveyor $1 is driven by the motorreduction gear: assembly 90. The oven 8-2 and the cooling chamber 83 arearranged to enclose the intermediate portions of the upper run of theconveyor and sized so that the racks 28'- may be drawn therethrough.Suitable heating means may be provided in the oven 82 in order to engulfthe molding units and racks in a heating media, and a blower 91 y beprovided on the top of the cooling chamber: 83

for forcing circulated cool air or room temperature air through themolding units. At the discharge end of the conveyor, the molding units29 may be removed from the racks 28 and placed on a table 92 Where themolds may be disassembled and the completed hollow articles removedtherefrom. Then the molds may be reassembled and reinserted in the rackand carried around to the inlet end of the oven 82 whereupon the moldingunits may be removed and placed upon a filling table 93 to be filled bya filling unit 9 and reassembled and reniserted into the racks 28 priorto the racks being advanced into the oven '82. It may be appreciatedthat the refilling process may take place also at the discharge end ofthe conveyor after the hollow plastic articles have been unloaded fromthe molding units. This embodiment merely illustrates that the racks 28might be utilized in connection with an endless conveyor in order tofurther mass produce the hollow plastic articles. It should beappreciated that the racks are rotatably mounted on the conveyor, andany suitable means may be provided to rotate the racks through 180revolutions during the molding process.

The method of molding the hollow plastic articles is somewhatillustrated in the FIGS. 7 to 15 which illustrate the steps of operationafter the plastic has been injected into the molds. A predeterminedquantity of liquid plastic, such as a vinyl resin, is first injectedinto the lower half of the mold. The mold is then closed by placing theupper half of the mold in mating relationship with the lower half, asshown diagrammatically in FIG. 7. Then the mold is subjected to heat asby insertion into the oven 17 in order to raise the temperature of thethermosetting plastic and commence the curing process. The mold is thenrotated through 180" revolutions at a speed which will centrifugallyhold the liquid plastic in the lower half of the mold until it reachesthe upper dwell position. As seen in FiG. 8, the position of the plasticat the instant the rotation has been concluded will be in the lower halfof the mold, which is now in the upper position. The mold is then heldstationary for a predetermined time in this position, during which timethe liquid runs down the inner surfaces of the mold and to the upperhalf 51 of the mold which is now in the lower position. FIG. 9illustrates how the plastic commenced flowing down the inner surface ofthe mold, and FIG. '10 illustrates approximately the extent of flow ofthe plastic prior to the time that the mold is again subjected to a 180revolution to the position shown in FIG. 11. Once again, the majority ofthe plastic will how to the then lower half of the mold, as seen inFIGS. 12 and 13, until it is time to again rotate the mold through a 180revolution. FIG. 14 is illustrative of the again upside down conditionof the mold, while FIG. 15 shows still another rotated position andapproximately how the completed article, which may be designated by thenumeral 95, has been formed within the mold. Of course, it will beappreciated that it will require a considerable number of revolutions inorder to completely cure the plastic within the mold. It has been foundthat a six-second interval is suflicient to allow between rotation ofthe molds for a common vinyl resin plastic.

The thermo-setting plastic is initially injected into the mold at roomtemperature and commences curing when it reaches a certain temperature.For example, it may be necessary to heat the plastic to a temperaturebetween 350 F. and 700 F. in order for it to properly set and cure.Further, after the plastic has properly cured, the molds are removedfrom the oven 17 and properly cooled to a temperature of approximately250 F. on the cooling table 43. Plastic should be cooled to atemperature so that it will not stretch and deform when removing thehollow plastic articles from the molds.

The number of cycles through which the mold will be rotated depends uponthe type of thermo-setting plastic used and its curing temperature, thewall thickness of the object being molded, and the wall thickness of themold.

Also, the dwell time between rotations of the mold may vary, althoughsix seconds has been found to be most favorable. It has been found thatsome vinyl resins properly cure after fifteen minutes of operation in anoven.

This application is a division of my copending application Serial No.815,974, filed May 26, 1959, now Fatent No. 3,048,896 granted August 14,1962.

It will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention, but it is understood that this application is to be limitedonly by the scope of the appended claims.

The invention is hereby claimed as follows:

1. Apparatus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of open ended carriagesrotatably supported in said oven and adapted to slidably receive moldingunits, openings in said oven opposite the open end of said carriages,doors covering said openings, means for intermittently rotating saidcarriages along horizontal axes through a cool ing table extending fromthe oven beneath said doors for receiving said molding units, and meanscarried by said table for cooling the molding units when they areremoved from the oven.

2. Apparatus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of shafts bearingly supportedabout horizontal axes on one Wall of the oven so that one end of eachshaft extends into the oven and the other end of each shaft extendsexternally of said oven, a rack carried on each shaft within said ovenand adapted to removably receive a molding unit, an opening in said ovenopposite each rack, a door covering each opening, and means forintermittently rotating said shafts through 180.

3. Apparatus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of shafts bearingly supportedabout horizontal axes on one wall of the oven so that one end of eachshaft extends into the oven and the other end of each shaft extendsexternally of said oven, a rack cantileverly mounted on the end of eachshaft extending into said oven for removably supporting a molding unit,means driving the other end of the shaft intermittently through 180, anopening in said oven opposite each rack, and a door covering eachopening.

4. Ap aratus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of shafts bearingly supportedabout horizontal axes on one wall of the oven so that one end of eachshaft extends into the oven and the other end of each shaft extendsexternally of said oven, a rack cantileverly mounted on the end of eachshaft extending into said oven for removably supporting a molding unit,a pinion gear mounted on the other end of each shaft, means engaging allof said pinion gears for driving the shafts intermittently through 180,an opening in said oven opposite each rack, and a door covering eachopening.

5. Apparatus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of shafts bearingly supportedabout horizontal axes on one wall of the oven so that one end of eachshaft extends into the oven and the other end of each shaft extendsexternally of said oven, a rack cantileverly mounted on the end of eachshaft extending into said oven for removably supporting a molding unit,a pion gear mounted on the other end of each shaft, a rack gear engagingall of said pinion gears, means for intermittently reciprocating saidrack gear to drive the shafts through 180, an opening in said ovenopposite each rack, and a door covering each opening.

6. Apparatus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of shafts bearingly supportedabout horizontal axes on one wall of the oven so that one end of eachshaft extends into the oven and the. other end of each shaft extendsexernally of said oven, a rack cantileverly mounted on the end of eachshaft extending into said oven for slidably supporting a molding unit, apinion gear mounted on the other end of each shaft, a rack gear engagingall of said pinion gears, a pneumatic cylinder drivingly connected toone end of said rack gear for intermittently reciprocating said rackgear and driving the shafts through 180, an opening in said ovenopposite each rack, and a door covering each opening.

7. Apparatus for molding hollow plastic articles comprising an oven,means for heating the oven, a plurality of shafts bearingly supportedabout horizontal axes on one Wall of the oven so that one end of eachshaft extends into the oven and the other end of each shaft extendsexternally of said oven, a rack cantileverly mounted on the end of eachshaft extending into said oven for slidably' supporting a molding unit,a pinion gear mounted on the opening in said oven opposite each rack,and a door covering each opening.

References Qited in the file of this patent UNITED STATES FATENTS2,629,131 Martin et a1 Feb. 24, 1953 2,834,986 Bailey et a1 May 20, 19582,874,964 Edwards Feb. 24, 1959

1. APPARATUS FOR MOLDING HOLLOW PLASTIC ARTICLES COMPRISING AN OVEN,MEANS FOR HEATING THE OVEN, A PLURALITY OF OPEN ENDED CARRIAGESROTATABLY SUPPORTED IN SAID OVEN AND ADAPTED TO SLIDABLY RECEIVE MOLDINGUNITS, OPENINGS IN SAID OVEN OPPOSITE THE OPEN END OF SAID CARRIAGES,DOORS COVERING SAID OPENINGS, MEANS FOR INTERMITTENTLY ROTATING SAIDCARRIAGES ALONG HORIZONTAL AXES THROUGH 180*, A COOLING TABLE EXTENDINGFROM THE OVEN BENEATH SAID DOORS FOR RECEIVING SAID MOLDING UNITS, ANDMEANS CARRIED BY SAID TABLE FOR COOLING THE MOLDING UNITS WHEN THEY AREREMOVED FROM THE OVEN.